Growth Mechanism Of Nanoparticles Research Articles

The formation mechanism of bimetallic PtRu alloy nanoparticles in solvothermal synthesis

An understanding of the nucleation and growth mechanism of bimetallic nanoparticles in solvothermal synthesis is important for further development of nanoparticles with tailored nanostructures and properties. Here the formation of PtRu alloy nanoparticles in a solvothermal synthesis using metal acetylacetonate salts as precursors and ethanol as both the solvent and reducing agent has been studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXRD). Unlike the classical mechanism for the synthesis of monodisperse sols, the nucleation and growth processes of bimetallic PtRu nanoparticles occur simultaneously under solvothermal conditions. In the literature co-reduction of Pt and Ru is often assumed to be required to form PtRu bimetallic nanocrystals, but it is shown that monometallic Pt nanocrystals nucleate first and rapidly grow to an average size of 5 nm. Subsequently, the PtRu bimetallic alloy is formed in the second nucleation stage through a surface nucleation mechanism related to the reduction of Ru. The calculated average crystallite size of the resulting PtRu nanocrystals is smaller than that of the primary Pt nanocrystals due to the large disorder in the PtRu alloyed structure.

Facile Method to Tune the Particle Size and Thermal Stability of Magnetite Nanoparticles

Nucleation and growth mechanism of iron oxide nanoparticles on zeolite template and their stability dependence are reported. Hyperfine field resulting from the variation of particle size indicates the effect of zeolite on particles growth; particle size decreases at lower concentration of zeolite. At higher concentration, a fraction of nano Fe3O4 experiences hyperfine field (45 and 49 T) similar to bulk particles. Effect of incubation and digestion time on the particles growth and the binding effect with zeolite are discussed. Annealing treatments show that the binding of nanoparticles with zeolite stabilizes the nanoparticles with regard to agglomeration and structural transformation. Thermogravimetry-differential thermal analysis (TG-DTA) shows that increase in dehydration temperature from 335.1 to 351.7 K results in zeolite content increasing from 0 to 1000 mg. Weight loss of the particles prepared in incubation time of 0.5 min is 9.46% and reaches 13.9% in 240 min. The weight loss remains practically constant at ca. 9% irrespective of the digestion method.

In situ total X-ray scattering study of the formation mechanism and structural defects in anatase TiO2 nanoparticles under hydrothermal conditions

The in situ PDF method provides detailed information about the formation and growth mechanisms of TiO2 anatase nanoparticles under hydrothermal conditions.

Growth mechanism of bioglass nanoparticles in polyacrylonitrile-based carbon nanofibers

Polyacrylonitrile (PAN) electrospinning in combination with sol–gel method has been a common technique to produce inorganic nanoparticles containing composite carbon nanofibers (CNFs) for diverse applications. To investigate the morphology evolution and crystal transformation of inorganic components along with CNF formation, bioactive glass (BG) containing CNFs (CNF/BG) were prepared by sintering as-spun PAN/precursor composite nanofibers in a nitrogen atmosphere at temperatures of 800, 1000 and 1200 °C. Comprehensive characterizations were performed with TEM, SEM-EDXA and XRD. For samples sintered at 800 °C, numerous BG nanoparticles were observed inside the CNFs and mainly in an amorphous state. With the sintering temperature raised to 1000 °C, a number of spherical BG nanoparticles were detected on the surface of the resulting CNFs, with a crystal structure of wollastonite (β-CaSiO3) polycrystals. When the samples were sintered at 1200 °C, the BG nanoparticles on the surface of CNFs merged into forms with cuboid-like geometry, mainly consisting of pseudowollastonite (Ca3(Si3O9)) single crystals. Based on the geometry evolution and dynamic size distribution function analyses (Ostwald ripening and Smoluchowski equations), it was concluded that the growth of BG nanoparticles conformed to the ripening mechanism at 800 °C and migration–coalescence mechanism at 1200 °C, while the process involved both ripening and migration–coalescence mechanisms at 1000 °C.

Magnetic graphene oxide nanocomposites: nanoparticles growth mechanism and property analysis

The growth mechanism of magnetic nanoparticles (NPs) in the presence of graphite oxide (GO) has been investigated by varying the iron precursor dosage and reaction time (product donated as MP/GO). The synthesized magnetic NPs were anchored on the GO sheets due to the abundant oxygen-containing functionalities on the GO sheets such as carboxyl, hydroxyl and epoxy functional groups. The introduced NPs changed the intrinsic functionalities and lattice structure of the basal GO as indicated by FT-IR, Raman and XRD analysis, and this effect was enhanced by increasing the amount of iron precursor. Uniform distribution of NPs within the basal GO sheets and an increased particle size from 19.5 to 25.4, 31.5 and 85.4 nm were observed using scanning electron microscope (SEM) and transmission electron microscope (TEM) when increasing the weight ratio of GO to iron precursor from 10:1, to 5:1, 1:1 and 1:5, respectively. An aggregation of NPs was observed when increasing the iron precursor dosage or prolonging the reaction time from 1 to 8 h. Most functionalities were removed and the magnetic NPs were partially converted to iron upon thermal treatment under a reducing condition. The GO and MP/GO nanocomposites reacted for one and two hours (denoted as MP/GO1-1 h and MP/GO1-2 h) were converted from insulator to semiconductor after the annealing treatment as annealed GO (A-GO, 8.86 S cm−1), annealed MP/GO1-1 h (A-MP/GO1-1 h, 7.48 × 10−2 S cm−1) and annealed MP/GO1-2 h (A-MP/GO1-2 h, 7.58 × 10−2 S cm−1). The saturation magnetization was also enhanced significantly after the annealing treatment, increased from almost 0 to 26.7 and 83.6 emu g−1 for A-MP/GO1-1 h and A-MP/GO1-2 h, respectively.

Controlled Growth of ZnO Nanoparticles with Different Morphologies Using Sol-Gel Technique

A low temperature sol-gel approach was demonstrated to prepare ZnO nanoparticles with controlled morphologies. By changing the concentration of NH4OH, the ZnO nanoparticles evolves from sphere-like, star-like and sheet-like structures. No peak of additional phase was observed in the XRD patterns except the diffraction peaks of ZnO. The estimated crystallite size of ZnO nanoparticles decreases with the increase of NH4OH. It is also found that the morphology of nanoparticles affects the optical bandgap of ZnO. The optical bandgap of sphere-like,star-like, and sheet-like ZnO nanoparticles are 3.55 eV, 3.48 eV and 3.45 eV, respectively. The growth mechanism of ZnO nanoparticles was discussed.

Influence of the pH on the ZnO nanoparticle growth in supercritical water: Experimental and simulation approaches

In order to improve the knowledge on the nucleation and the growth mechanisms of metal oxides nanoparticles produced in supercritical water domain, ZnO was used as a “model” material. A continuous process of hydrothermal synthesis was employed to synthesize ZnO nanopowders (T=410°C and P=305bar) from Zn(NO3)2 and KOH solutions with different values of [KOH]/[Zn(II)] ratio from 0 to 8 in order to investigate the pH effect on the growth of ZnO nanocrystallite in terms of size and morphology. The samples were characterized by X-Ray Diffraction and Transmission Electronic Microscopy. ZnO crystal was considered as a cylindrical crystallite with a diameter D and height H. Especially, the aspect ratio D/H was already used to observe the change of ZnO nanoparticle shape correlated with TEM observations and results from a CFD simulation model. A schematic synoptic of the ZnO growth in supercritical domain is also presented.

Growth mechanisms of self-assembled gold nanoparticles in Deep Eutectic Solvent

Self-assembled metallic nanoparticles are attractive candidates for plasmonic heating, non-linear optical switching [1], bio-analytical, chemical [2], catalytic , and surface enhanced RAMAN scattering (SERS) [3]. These applications are strongly dependent on the shape, size, composition, size distribution and volume fraction of nanoparticles. Here, self-assembly of gold nanoparticles (AuNPs) was obtained by low energy sputter deposition on Deep Eutectic Solvent (DES ; choline chloride and urea) surfaces and elucidated by Small Angle X-ray Scattering (SAXS), Cryogenic Transmission Electron Microscopy (Cryo-TEM) and UV-Vis. Data analysis shows the formation of spherically shaped AuNPs of 5 nm in diameter with narrow size distributions. Moreover, analysis reveals that prolongation of gold-sputtering time has no effect on the size of the particles and only the concentration of AuNPs increases linearly. The growth of the maxima in evaluated structure factor S(q) and the distance distribution function G(r) at higher concentrations of AuNPs is caused by the interference effects. Moreover, it indicates that the particles are not arranged in random but have a self-assembly in short-range order. Prolonged gold-sputtering time leads to increase in the ordering of the AuNPs with strong interactions. It is proposed that the self-assembly of AuNPs is due to the ionic liquid template effects of DES and the balancing physical forces. Moreover, a disulfide based stabilizer bis ((2-Mercaptoethyl) trimethylammonium) disulfide dichloride was applied to supress the self-assembly. The stabilizer even reverses the self-assembled or agglomerated AuNPs back to stable 5 nm individual particles. The templating effect of DES is compared with the non-templating solvent Castor oil. Our results will also pave a way to understand and control self-assembly of metallic and bimetallic nanoparticles.

Precision synthesis: designing hot spots over hot spots via selective gold deposition on silver octahedra edges.

A major challenge in plasmonic hot spot fabrication is to efficiently increase the hot spot volumes on single metal nanoparticles to generate stronger signals in plasmon-enhanced applications. Here, the synthesis of designer nanoparticles, where plasmonic-active Au nanodots are selectively deposited onto the edge/tip hot spot regions of Ag nanoparticles, is demonstrated using a two-step seed-mediated precision synthesis approach. Such a "hot spots over hot spots" strategy leads to an efficient enhancement of the plasmonic hot spot volumes on single Ag nanoparticles. Through cathodoluminescence hyperspectral imaging of these selective edge gold-deposited Ag octahedron (SEGSO), the increase in the areas and emission intensities of hot spots on Ag octahedra are directly visualized after Au deposition. Single-particle surface-enhanced Raman scattering (SERS) measurements demonstrate 10-fold and 3-fold larger SERS enhancement factors of the SEGSO as compared to pure Ag octahedra and non-selective gold-deposited Ag octahedra (NSEGSO), respectively. The experimental results corroborate well with theoretical simulations, where the local electromagnetic field enhancement of our SEGSO particles is 15-fold and 1.3-fold stronger than pure Ag octahedra and facet-deposited particles, respectively. The growth mechanisms of such designer nanoparticles are also discussed together with a demonstration of the versatility of this synthetic protocol.

“One-Stone–Two-Birds” Modulation for Na3ScF6-Based Novel Nanocrystals: Simultaneous Morphology Evolution and Luminescence Tuning

Control over the morphology, size, and crystallographic phase of nanocrystals (NCs) through impurity doping is central to the realization of their unprecedented or improved properties. Herein we present the “one-stone–two-birds” modulation including simultaneous modification of the morphology and tuning of the luminescence for Na3ScF6 based NCs via a simple doping strategy. Ce3+/Tb3+ codoped Na3ScF6 NCs with monoclinic structure and hexagonal nanoplate or nanorod morphology were obtained through a modified solvothermal method. The formation of monodisperse Na3ScF6-based NCs with diverse architectures closely correlates with the doping level of Tb3+. On the basis of the experimental results, the possible growth mechanism for nanoparticles is proposed. Under UV light excitation, Na3ScF6:Ce3+/Tb3+ samples exhibited characteristic emissions from both Ce3+ and Tb3+ ions. By proper variation of the amount of Tb3+ doping while maintaining Ce3+ concentration, the emission color tuned from blue to green accompanie...

Deep eutectic solvents for the self-assembly of gold nanoparticles: a SAXS, UV-Vis, and TEM investigation.

In this work, we report the formation and growth mechanisms of gold nanoparticles (AuNPs) in eco-friendly deep eutectic solvents (DES; choline chloride and urea). AuNPs are synthesized on the DES surface via a low-energy sputter deposition method. Detailed small angle X-ray scattering (SAXS), UV-Vis, and cryogenic transmission electron microscopy (cryo-TEM) investigations show the formation of AuNPs of 5 nm diameter. Data analysis reveals that for a prolonged gold-sputtering time there is no change in the size of the particles. Only the concentration of AuNPs increases linearly in time. More surprisingly, the self-assembly of AuNPs into a first and second shell ordered system is observed directly by in situ SAXS for prolonged gold-sputtering times. The self-assembly mechanism is explained by the templating nature of DES combined with the equilibrium between specific physical interaction forces between the AuNPs. A disulfide-based stabilizer, bis((2-mercaptoethyl)trimethylammonium) disulfide dichloride, was applied to suppress the self-assembly. Moreover, the stabilizer even reverses the self-assembled or agglomerated AuNPs back to stable 5 nm individual particles as directly evidenced by UV-Vis. The template behavior of DES is compared to that of nontemplating solvent castor oil. Our results will also pave the way to understand and control the self-assembly of metallic and bimetallic nanoparticles.

Time-Resolved Small-Angle X-ray Scattering Study on the Growth Behavior of Silver Nanoparticles

Silver nanoparticles were prepared with a chemical reduction method in the presence of polyvinylpyrrolidone (PVP) used as a stabilizing agent. During the synthesis of Ag nanoparticles, aqueous silver nitrate solutions were used as the precursors and sodium borohydride was used as the reducing agent. Four Ag-nanoparticle suspensions were prepared with the initial Ag+ concentrations of 2, 4, 6, and 8 mM in the corresponding precursors. The in-situ time-resolved small-angle X-ray-scattering (SAXS) technique was used to monitor the nucleation and growth processes of Ag nanoparticles. The particle-size change with time was obtained by analyzing the SAXS data with a tangent-by-tangent method. The SAXS results demonstrate that the Ag nanoparticle growth behaves as a linear relation in the initial growth stage (<1 s), which was used to evaluate the critical particle size. The growth of Ag nanoparticles experienced a fast stage and then a slow stage in their whole formation process. A diffusion–coalescence model has been proposed to describe the growth behavior. The particle size change with growth time can be fitted well by this model. The effect of initial Ag+ concentration on the final particle size and the growth mechanism of Ag nanoparticles are discussed in this paper.

Synthesis and Optical Characteristics of PAM/HgS Nanocomposites

Polyacrylamide (PAM) -HgS nanocomposites were successfully prepared in polyacrylamide (PAM) matrix. From TEM and XRD characterizations, the synthesized HgS nanocrystals were chain-like spherical in shape with a diameter of about 40-60 nm and high crystalline quality. The quantum-confined effect of HgS nanocrystals was confirmed by UV-vis diffuse reflection spectra. The optical properties of products were investigated by using photoluminescence (PL) spectra, which showed that HgS nanocrystals exhibited good optical properties with maximum emission peak at about 640 and 650 nm at different reaction temperatures. The interaction of HgS nanocrystals with PAM was studied through FT-IR spectroscopy and TG analysis, which suggested that <TEX>$Hg^{2+}$</TEX> could interact with functional groups of PAM. The experimental results indicated that PAM not only induced nucleation, but also inhibited further growth of HgS crystals and play an important role in the formation of PAM/HgS nanocomposites. In addition, the possible mechanism of HgS nanoparticles growth in PAM solution was also discussed.

Magnetic behavior of doped VO2 nanoparticles

Nanoparticles of vanadium dioxide doped with chromium and iron are obtained using the hydrothermal technique. Their morphology is studied by means of TEM and XRD. The temperature dependence of their magnetic characteristics is investigated using the magnetic susceptibility method, and the parameters of exchange interaction between magnetic atoms are estimated. It is shown that the introduction of a doped element changes the mechanism of nanoparticle growth and lowers the temperature of the semiconductormetal transition to 150–200 K.

Hydrothermal synthesis, characterization, and growth mechanism of hematite nanoparticles

Polyhedron-shaped hematite (α-Fe2O3) nanoparticles have been successfully synthesized via a facile hydrothermal method by mixing FeCl3 and NH4OH at high temperature. In this work, the influences of experimental conditions such as the effects of the concentration of iron’s ion, NH4OH concentration, and reaction temperature on the hematite’s particle size, dispersity, and growth rate were investigated. Results show that hematite nanoparticles with good crystallinity with the particle size of 100 nm could be obtained when the hydrothermal reaction was carried out with concentration of Fe3+ = 16 mM, NH4OH = 40 mM, reaction temperature = 120 °C, and reaction time = 24 h. In addition, this study investigates the hematite nanoparticle-formation mechanism with reaction time. It is observed that the formation of hematite nanoparticles are initiated by the formation of intermediate phase of goethite nanorods in the early stage of hydrothermal reaction, which further transform into hematite crystal as the reaction is progressed.

Synthesis of nanomaterials by continuous-flow microfluidics: a review.

The development of controlled synthesis protocols of nanostructured materials with tailored particle size and shape has been a significant research area in nanoscience and nanotechnology. Much innovative research efforts had been focused on finding suitable chemical reagents and synthetic methodologies that offer opportunities to produce the desired structure-function controlled nanomaterials. On the other hand, the reactor equipment for the synthesis of these tailored nanomaterials is of prime importance not only at laboratory-scale but also with view of up-scaling the synthetic processes into large-scale productions. Whilst the sequential three-stage scale-up from the conventional process (i.e., lab-scale/pilot-scale/large-scale) using multi-purpose batch reactor is masked with complications, on the other hand, the interface of nanomaterials synthesis processes and continuous-flow microfluidic chemistry has demonstrated relatively superior process performance over conventional technologies. Consequently, the uses of continuous-flow microfluidics systems have recently attracted much research attention as versatile tools for the synthesis of various structured nanomaterials. In this review, we highlight and analyze the key achievements to date of adopting microfluidics technologies for the controlled synthesis of nanomaterials with well-defined structural properties desirable for the intended applications. We devote the significant emphasis on demonstrating the improved potential characteristics features of continuous-flow microfluidics as a capable technology to provide efficient synthesis processes for the production of various nanosized scale structured materials with precise control of the involved chemistry. Moreover, we discuss the novel process window opportunities of hyphenated microfluidics nanoparticles synthesis with the in-situ or in-line structure characterization during synthesis under real-time reaction conditions which provide interesting insights and experimental evidence on nanoparticle growth mechanisms.

Morphology tuning of mono-disperse silver nanoparticles by reaction temperature adjustment

Mono-disperse silver nanoparticles with tunable morphologies have been fabricated by reducing AgNO3 in the presence of N-dimethylformamide (DMF) and larger molecular weight poly (vinylpyrrolidone) (PVP). By adjusting the reaction temperature, the conversion of the morphology can be easily and effectively controlled. The crystal structures and growth mechanism of mono-disperse silver nanoparticles were studied by using TEM, HR-TEM, FFT, XRD and UV-Vis spectra data. The results show that the morphologies of nanoparticles with spherical shape can be adjusted to a truncated triangle/hexagon along with the change of reaction temperature from 80 to 120 °C. It is found that the shape transformation from sphere to truncated triangle is caused by the difference in surface energy and the selective adsorption of PVP on silver atom.

CdSe/CdS核壳纳米晶微波水热法一步合成与发光光谱分析

CdSe /CdS core-shell nanocrystals were one-step prepared by microwave-hydrothermal method.The growth mechanism of nanoparticles was discussed and attributed to the sulfur release process from mercaptopropionic acid.The results from XRD and Raman spectra suggested that the core-shell CdSe /CdS nanocrystals were obtained under the reaction temperature of 140 ℃.FTIR spectra were in situ monitored for the decomposition of mercaptopropionic acid upon reaction time,which contributed to the formation of CdS shells.The band-related and trap states fluorescent emission from nanocrystals were both observed in PL spectra.The increased band related emission intensity further verified the formation of core /shell structure of CdSe nanocrystals.

Synthesis and Characterization of Cobalt Nanoparticles Using Hydrazine and Citric Acid

Cobalt nanoparticles were produced by employing the liquid-phase reduction method and hydrazine. The effect of citric acid additives on the formation and growth mechanism of cobalt nanoparticles was investigated using polarization methods. The cobalt nanoparticles produced in 0.2 M cobalt sulfate and 5 M hydrazine at 298 K had a spherical shape with a diameter of 400 nm. The dendritic nanoparticles formed with the decreasing of hydrazine concentration at 298 K. On the other hand, dendritic large particles are confirmed at 353 K. It was confirmed that the reduction reaction progressed with the addition of citric acid, and a hexagonal close-packed (εCo) phase was formed.

A facile additive-free method for tunable fabrication of UO2 and U3O8 nanoparticles in aqueous solution

Spherical UO2 nanoparticles with an average diameter varying from 30 to 250 nm and U3O8 nanocuboids with a width of 400 nm and a length of 1 μm have been successfully synthesized just by a simply additive-free hydrothermal synthesis method. To selectively obtain the phase-pure U3O8 and UO2 nanoparticles, the experimental conditions, such as the solution pH and temperature as well as the concentration of hydrazine, have been established and optimized. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In order to investigate the growth mechanism of the uranium oxide nanoparticles, XRD, SEM and Fourier transform infrared (FT-IR) spectrum measurements were carried out for the precursors prepared at different pH and hydrothermal time. The crucial factor for tunable fabrication of uranium oxide nanoparticles could come from the different reducing ability of hydrazine at various solution pH.